In this specification, the term “air-conditioners” generally and collectively means air heating, cooling and conditioning devices, apparatuses, systems and installations for succinctness unless the context requires otherwise. Likewise, the term “air-ventilators” generally and collectively means air-ventilating or air-circulating means, devices, systems or installations for succinctness, unless the context otherwise requires.
Air-conditioners are widely used to provide a comfortable indoor environment for occupants of residential, commercial or public buildings, premises or other enclosed spaces such as offices, schools, cinemas, theatres, halls, and other similar places. Air-ventilators are always used in or with air-conditioners so that indoor air, which may contain a lot of harmful gases, can be constantly and regularly replaced with out-door air supply which generally has a higher oxygen content and a lower harmful gas content. Typical harmful gases found in enclosed buildings, especially crowded buildings, include carbon-dioxide, carbon-monoxide, unpleasant odors, irritants such as formaldehyde in the building materials and the radioactive radon gas released from granite.
On the other hand, although out-door air generally has a higher oxygen content, it is not without pollutants and air-pollution is especially bad in urban built-up areas. Typical pollutants found in out-door air include particulate pollutants such as dusts, ashes, smoke particles, particles from incomplete combustion of diesel fuel, pollens, odors, acid or other chemical gases, and bacterial organisms.
In order to block, or at least minimise, the entrance of harmful substances into an enclosed indoor space to provide a healthier indoor environment, air-ventilators of air-conditioners are usually provided with air filters at the “fresh-air” intake ports. The air filters are usually simple mesh filters, although the more sophisticated filters such as activated carbon filters, polymeric foam filters, glass fiber filters and biostat filters such as those containing potassium permanganate are useful alternatives or additions. In some applications, high-efficiency particulate air (HEPA) filters which are known to be effective to remove up to 99.7% of air-borne particles of the size of 0.3 microns or larger, can be used. Some air filters for use in air-ventilators may include one or more types of filtering materials and designs in order to optimally removed different types of harmful substances from the supply air.
Since the conditioned indoor air which is to be exhausted contains thermal energy which can be re-used, heat exchangers which provide means for transferring thermal energy between the in-coming and the out-going air streams are known to have been used in air-ventilators. Examples of such ventilators are described in the following U.S. patents: U.S. Pat. No. 5,238,052, U.S. Pat. No. 4,874,042, U.S. Pat. No. 4,377,400. Heat exchangers are utilized to recover thermal energy from the out-going air stream to reduce wasted thermal energy discharge from the exhaust air. This recouperation of energy is beneficial for the protection of the environment, as well as imposing a lesser load demand on the air-conditioners and, at the same time, reducing the operating and running costs of air-conditioners. Such benefits are achievable because it is known that thermal exchange between a cold air stream and a hot air stream will reduce the total energy requirement for conditioning the in-coming air stream. Thus, for an air-cooling system, the in-coming air stream is cooled by the out-going exhaust air before the exhaust air leaves the air-conditioner. Similarly, for an air-heating system, the out-going warm air is used to warm up the in-coming out-door air before it enters a building.
In light of the afore-mentioned requirements for contemporary air-conditioners, it is highly beneficial and desirable that air-conditioners incorporating thermal exchangers as well as highly efficient air filters are provided. However, it has been observed that conventional air-conditioners of this description do not have a high thermal efficiency, especially after pro-longed use. Hence, it is desirable that air-conditioners with air-ventilators having highly efficient air filters which at the same time has a high thermal efficiency and a stable performance can be provided.
Furthermore, while air-conditioners are widely used in many crowded places such as schools to provide a better indoor environment, their performance in the exchanging of stale indoor with fresh out-door air is not entirely satisfactory. In fact, there have been reports that the indoor carbon-dioxide concentration in many air-conditioned schools exceeds the generally acceptable level of 800 ppm by as much as 35%. Hence, it is desirable that highly thermal efficient air-ventilators can be installed to supplement the supply of out-door air into the enclosed indoor space without substantially increasing energy costs or wasted energy.
It is therefore desirable to provide air-ventilators with high efficiency air filters which operate with high thermal efficiency and low running costs so that the environment can be protected, wasted heat as well as energy costs can be reduced. As space is precious in the city, it is also desirable that the improved air-ventilators can be provided in a compact design. Preferably, important components, such as the thermal exchanger unit, of the air-ventilators are of modular design for easy maintenance. In addition, while the air-ventilator can be used as a stand-alone unit, it is desirable that the improved air-ventilators can be incorporated or used in or with air-conditioners.